The low resistance value of a shunt resistor results in very small voltage measurements as low as 3 μV. To minimize the measurement error from parasitic voltages developed by dissimilar metals and temperature gradients, the conductor materials used in connection with a shunt resistor shall be the same metallic elements. The parasitic voltages can also be minimized by eliminating the temperature differences between the various parts of the circuit as these temperatures can contribute to measurement error in the application.
Current solutions accomplish the connection between the shunt resistor and the substrate supporting the electronic components by soldering as shown in U.S. Pat. No. 6,787,935 granted to Andreus Heim Sep. 7, 2004, or by using scythe-type lines bent upward by 90 degrees of the transmission connections. Alternatively, the connection between the shunt resistor and the substrate can be accomplished by soldering S-shaped copper interconnects as shown in the prior art assembly of FIG. 1 which is described in more detail below. This latter connection method provides stress relief to allow for mismatch between the expansion rates of the substrate and the shunt material.
The weakness of these connection methods is that the soldered interfaces induce voltage measurement error. Moreover the connection methods are difficult to process because significant energy is required to heat the large copper slug sufficiently to reflow solder. The voltages induced by the various metals involved in the connection are increased by the thermal differences between the metals. Since the voltages that are to be measured across the shunt resistor are very small (as low as 3 μV), the induced voltages can significantly affect the accuracy of the shunt voltage measurement.